Blog of Web Developer Garry Pilkington

(ASP.Net, C#, AngularJs, JavaScript, HTML5 & UWP)

Wow what a title, but it does explain that this post covers debugging the full .net framework application (not .net core) running on a Server Core container (not Linux) from the comfort of a Windows 10 Pro machine running Visual Studio 2015 and Docker for Windows.

Running remote tools on a machine and attaching is a pretty straight forward task, but there a re a few hurdles in the way when doing it on Windows Server Core 2016 container, but once it is scripted it is pretty painless.

Firstly we need a decent Docker image to start with, luckily the guys at Microsoft have created the Microsoft/aspnet image we can start with so lets build up our dockerfile

FROM microsoft/aspnetRUN mkdir C:\site

This gets the base image and creates directory that we are going to use for our web files.

This section is completely optional and all it does is install the web management tools for remote administration. You may want to tweak the container settings such as application pool and start and stop it from the GUI on your Windows 10 machine. If you are not bothered about IIS settings, then you can omit this section.

This copies the directory permissions set up for the wwwroot directory and assigns it to the site directory, so we don’t end up with nasty permission denied issues.

EXPOSE 8000 8172 4020 4021

We need to expose 8000 for our web application, 8172 for remote IIS admin and 4020 and 4021 are the ports we need opening for remote debugging tools. Visual Studio 2015 remote tools use these ports, other versions use different ports and as yet I cannot find the ports for Visual Studio 2017.

Next we locate our dockerfile using a cmd prompt and run docker build

docker build -t iis-site .

It will take a while to run through and will be quicker in future builds as you will already have the layers that make up the final image.

This creates a container based on our previous iis-site image and creates a mapping to a directory on our Windows 10 machine to the site directory we created in the dockerfile; this container will have the name web1.

This gives me 172.19.184.110 and yours will be different as each container gets its own address. We know we are on port 8000 so open up a browser and browse to your home page:-

Great, now lets get debugging. In future releases of Visual Studio 2017 it will be possible to debug straight into a Windows container, but at the moment it is limited to Linux containers, so we need to do a bit more configuration.

Once downloaded, put the .exe in the same directory as your web application on your machine as that is already visible to the container. There are ways to automate the download using Invoke-WebRequest, but I had several issues with resolving the url so it was easier to do it myself.

Create a .bat file with the following and copy that also into the web application directory on your machine:-

rtools_setup_x64.exe /install /quiet

Get the id of the container by using the command:-

docker ps

With the id, lets open an interactive cmd prompt:-

docker exec -it 03a8eb766d5a cmd

Where 03a8eb766d5a is my container identifier.

Run the bat file:-

install-tools.bat

This will take a couple of minutes to run through, but when it is finished you can cd to the C:\Program Files\Microsoft Visual Studio 14.0\Remote Tools directory to take a look.

This will start the remote debugging service msvsmon and your cmd prompt will just sit quiet with no cursor.

So now open up the web application in Visual Studio and go to Debug >> Attach to process

Click on the Find button and it should find your container with its id and ip address showing, simply select it.

Now we need to make sure we choose Managed (v4.6, v4.5, v4.0) code or whatever version of the framework you are using. Also make sure show processes from all users is checked.

Scroll down and choose w3wp and attach. Check the security warning and then start debugging as you would normally do.

Ideally it would be best if the remote tools could be downloaded as part of the build and the starting of msvsmon be automatic when F5 in Visual Studio. If you are happy with your container, you could save it as an image using the command:-